Those for stages and such are log windings. This is to allow
most of the travel around the circle as light dimming / bright'ing range.

I found that when repairing a stage set some years ago. They used
levers on a front panel and not knobs.

I have a large one in my general AC system. It must weigh 40 pounds.

I used 150 watt versions to control my electric trains 40 years ago.

Martin

On 10/10/2012 6:12 AM, Pete C. wrote:

"DoN. Nichols" wrote:

On 2012-10-10, Karl Townsend wrote:
Xmas came early this year, a couple a great big variacs showed up in
the mail today. Thank you Santa Pete.

These monsters have a common shaft so two can be turned in unison,
nice feature as i need to hook these up 220. Just want to verify the
hookup: The hot lead on each variac to each leg of the 220, the wiper
for each variac to the load, tie the nuetral on each variac together
and to nothing else (not ground that is). Correct?

I would tie the neutral of each together and to the supply
neutral for safety against imbalance. Otherwise, you have it right.

Note that many powerstats (these are not General Radio Variacs,
based on the photos -- use "variable autotransformer" for a generic
term) as well as genuine Variacs have extra taps, so you can boost the
line to something like 140 V with a 120 V input per autotransformer.
And because these can be wired to increase CW or CCW, they often have a
lower tap as well, so they are (in series) 20V, 100V and another 20V if
you want boost. You probably don't want boost.

Lighting control variacs don't have extra taps or "boost" capability,
just simple 0-120.